Rasmus actually doesn't train cardio at all, he doesn't believe in exerting himself in such a manner where there isn't a puck or some other thing of value to chase over. You can run on the treadmill all you want, but that isn't going to replicate the game situation of ripping down the ice. Instead, he goes through his day to day life and when he sees something, he sprints after it - walks for a couple seconds, then continues sprinting again. It's these short bursts in a situation where he feels that same desire for the puck that get his brain primed to be firing when he needs it to be on the ice. For example, you can sometimes see Rasmus hauling ass after an ice cream truck down the street on a hot day in LA. He's so far only bowled over two toddlers on his way down the street, but that's also going to get better as he improves his spacial awareness as he flies around.